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        <td class="header">&nbsp; Multilook</td>
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<h3>Multilook Operator</h3>
Generally, a SAR original image appears speckled with inherent speckle
noise.
To reduce this inherent speckled appearance, several images are
incoherently
combined as if they corresponded to different looks of the same scene.
This
processing is generally known as multilook processing. As a result
the&nbsp;multilooked image&nbsp;improves the image interpretability.
Additionally, multilook
processing can be used to produce an application product with nominal
image pixel size.<br>
<h4>Multilook Method</h4>&nbsp;&nbsp;&nbsp;There are two ways to implement the multilook processing:<br>
<ul>
    <li>The multilooked images
        can be produced by space-domain averaging of a single look image, either with
        or without specific 2D kernels by convolution.
    </li>
    <li>The multilook images can be produced by frequency-domain method using the sub-spectral band width.</li>
</ul>
&nbsp;&nbsp;&nbsp;This operator implements the space-domain multilook method by
averaging a single look image with a small sliding window.<br><h4>Selecting Range and Azimuth Looks</h4>&nbsp;&nbsp;&nbsp;In
selecting the number of range looks and the number of azimuth looks, user has two&nbsp;options:<br>
<ol>
</ol>
<ul>
    <li>GR square pixel: the user specifies the number of range looks while the number
        of azimuth looks is computed based on the ground range spacing and the azimuth
        spacing. The window size is then determined by the number of range looks and the
        number of azimuth looks. As a result, image with approximately square pixel spacing
        on the ground is produced.
    </li>
    <li>Independent looks: the number of looks in range and azimuth can be selected
        independently. The window size is then determined by the number of range looks
        and the number of azimuth looks.
    </li>
</ul>
<ol>
</ol>
<h4>Multilook Complex Product</h4>
<ul><li>When the input product is complex, if you want to multilook the
intensity image, you should select the intensity band by highlighting
it in the Source Bands window. If no bands are selected, then the I and
Q bands are selected by default and multilooked. The virtual intensity
band generated from the multilooked I and Q bands is NOT
the&nbsp;multilooked intensity band. &nbsp; </li><li>When the input is a complex interferogram product and
you are interested in multilooking the phase, you should NOT select the
phase band. Instead, you should select the I and Q bands. The desired
phase band is generated from the multilooked I and Q bands. Otherwise,
artefacts, such as the bell-shaped histogram, will be introduced in the
multilooked phase band.&nbsp;</li></ul><h4>Parameters Used</h4>&nbsp;&nbsp;&nbsp;The following parameters are used by the operator:<br>
<ol>
    <li>Source Band: All bands (real or virtual) of the source product. User can
        select one or more bands for producing multilooked images. If no bands are
        selected, then by default all bands are selected.
    </li>
    <li>GR Square Pixel: If selected, the number of azimuth looks is
        computed based on the user selected number of range looks, and range
        and azimuth spacings are approximately the same in the multilooked
        image.
    </li>
    <li>Independent
        Looks: If selected,&nbsp;the number of range looks and the number of
        azimuth looks are selected independently by the user.
    </li>
    <li>Number of Range Looks: The number of range looks.
    </li>
    <li>Number of Azimuth Looks: The number of azimuth looks.
    </li>
    <li>Mean GR Square Pixel: The average of the range and azimuth pixel spacings in the
        multilooked image. It is computed based on the number of range looks, the number of
        azimuth looks and the source image pixel spacings, and is available only when 'GR Square Pixel' is selected.
    </li>
    <li>Output
        Intensity: This checkbox is for complex product only. If
        not checked, any user selected bands (I, Q, intensity or phase) are
        multilooked and output individually. If checked, user can only select
        I/Q or intensity band and the output is multilooked intensity band.<br>
    </li>
    <ol>
    </ol>
</ol>
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<img style="width: 436px; height: 445px;" alt="" src="images/multilook_dlg.jpg"><br>

<p> Reference:&nbsp;Small D., Schubert A.,&nbsp;Guide to ASAR Geocoding, RSL-ASAR-GC-AD, Issue 1.0, March 2008</p>
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